Mitt Romney told Fox News today he will be too busy to appear at a Dec. 27 Republican presidential campaign debate in Iowa that will be moderated by Donald Trump. He joins U.S. Rep. Ron Paul and former Ambassador Jon Huntsman in declining the offer.

Former House Speaker Newt Gingrich and former U.S. Sen. Rick Santorum have accepted Trump’s invitation. U.S. Rep. Michele Bachmann and Texas Gov. Rick Perry are uncommitted.